Gamma radiation tests of potential optical fiber candidates for fibroscopy

Two pure silica core F-doped silica cladding multimode step-index (MMSI) fibers were selected and exposed to γ rays up to 1.5 MGy. One is a conventional polyimide coated high OH fiber (Suprasil(R) F-100 core material). The other is a new type of low OH low Cl aluminium coated fiber whose core material is made of KS-4V glass. Two successive irradiations, separated by a 3-days recovery time, were performed at 4.9 kGy/h and 60°C. Radiation-induced attenuation spectra were recorded in situ from 400 nm to 1200 nm using a white light source and an optical spectrum analyser. In the conventional fiber, the induced attenuation spectra were governed by the growth and the recovery of the 600 nm band associated to non-bridging oxygen hole centers (NBOHCs). By contrast, for doses higher than 100 kGy, the KS-4V fiber showed fairly dose and time-invariant spectra (attenuation values of few dB/m decrease with increasing wavelength in the visible range). Because of the absence of the 600 nm band, the KS-4V fiber, beside the conventional fiber, appears to be a very promising candidate for fibroscopy